What was done
O2/N2 measurements of a suite of tanks filled with background air collected at Cape Grim, Tasmania between April 1978 and January 1997 were used to derive mean rates of carbon storage in the world's oceans and the terrestrial biosphere over this 19-year time period.

What was learned
The results of the analysis suggest that "the terrestrial biosphere has been essentially in balance" with respect to surface fluxes of carbon over the period of study.  However, it is known from other studies that tropical deforestation has produced a huge net loss of carbon annually.  As a result, the authors are forced to acknowledge the existence of a terrestrial carbon sink of like magnitude.

What it means
In the words of the authors, "compensating growth of the [terrestrial] biosphere is implied," which they attribute to "reforestation, higher rates of net production in response to climatic trends, fertilisation by elevated levels of atmospheric CO2 or nitrogen deposition or a combination of these factors."  Hence, although the physician is often accused of failing to heal himself, the biosphere appears to be doing just fine in this regard, yearly re-sequestering all of the carbon that man takes out of it.  So, if man were to reduce the rate at which he is denuding the land of trees, it is clear that the forests of the world would begin to take a big bite out of the CO2 that we yearly put into the air as a consequence of the burning of fossil fuels.